/* J. David's webserver */
/* This is a simple webserver.
 * Created November 1999 by J. David Blackstone.
 * CSE 4344 (Network concepts), Prof. Zeigler
 * University of Texas at Arlington
 */
/* This program compiles for Sparc Solaris 2.6.
 * To compile for Linux:
 *  1) Comment out the #include <pthread.h> line.
 *  2) Comment out the line that defines the variable newthread.
 *  3) Comment out the two lines that run pthread_create().
 *  4) Uncomment the line that runs accept_request().
 *  5) Remove -lsocket from the Makefile.
 */
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <sys/stat.h>
#include <pthread.h>
#include <sys/wait.h>
#include <stdlib.h>

#define ISspace(x) isspace((int)(x))

#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"

void *accept_request(void *);
void bad_request(int);
void cat(int, FILE *);
void cannot_execute(int);
void error_die(const char *);
void execute_cgi(int, const char *, const char *, const char *);
int get_line(int, char *, int);
void headers(int, const char *);
void not_found(int);
void serve_file(int, const char *);
int startup(u_short *);
void unimplemented(int);

/**********************************************************************/
/* A request has caused a call to accept() on the server port to
 * return.  Process the request appropriately.
 * Parameters: the socket connected to the client */
/**********************************************************************/
// 连接客户端请求 参数 client 为客户端套接字
void *accept_request(void *client)
{
    char buf[1024];
    int numchars;
    char method[255];
    char url[255];
    char path[512];
    size_t i, j;
    struct stat st;
    int cgi = 0;      /* becomes true if server decides this is a CGI program */
    char *query_string = NULL;
	// 读取套接字的一行
    numchars = get_line(*((int *)client), buf, sizeof(buf));
    i = 0; 
	j = 0;
    while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) {
    	method[i] = buf[j];
    	i++; 
        j++;
    }
    method[i] = '\0';

    if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) {
    	unimplemented(*((int *)client));
        return NULL;
    }

    if (strcasecmp(method, "POST") == 0) {
        cgi = 1;
    }

    i = 0;
    while (ISspace(buf[j]) && (j < sizeof(buf))) {
        j++;
    }
    while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf))) {
        url[i] = buf[j];
        i++;
		j++;
    }
    url[i] = '\0';

    if (strcasecmp(method, "GET") == 0) {
        query_string = url;
		while ((*query_string != '?') && (*query_string != '\0')) {
            query_string++;
		}
		if (*query_string == '?') {
            cgi = 1;
            *query_string = '\0';
            query_string++;
		}
    }
    sprintf(path, "htdocs%s", url);
    if (path[strlen(path) - 1] == '/') {
		strcat(path, "index.html");
    }
    if (stat(path, &st) == -1) {
		while ((numchars > 0) && strcmp("\n", buf)) {  /* read & discard headers */
	    	numchars = get_line(*((int *)client), buf, sizeof(buf));
		}
		not_found(*((int *)client));
    }
    else {
		if ((st.st_mode & S_IFMT) == S_IFDIR) {
            strcat(path, "/index.html");
		}
		// 如果有执行权限，则认为是 .cgi 脚本
		if ((st.st_mode & S_IXUSR) || (st.st_mode & S_IXGRP) || (st.st_mode & S_IXOTH)) {
	    	cgi = 1;
		}
		if (!cgi) {
	    	serve_file(*((int *)client), path); 	// 发送 htdocs/index.html
		}
		else {
            execute_cgi(*((int *)client), path, method, query_string); 	// 执行 CGI 脚本
		}
    }
    close(*((int *)client));
    return NULL;
}

/**********************************************************************/
/* Inform the client that a request it has made has a problem.
 * Parameters: client socket */
/**********************************************************************/
void bad_request(int client)
{
    char buf[1024];
    sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "Content-type: text/html\r\n");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "\r\n");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "<P>Your browser sent a bad request, ");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "such as a POST without a Content-Length.\r\n");
    send(client, buf, sizeof(buf), 0);
}

/**********************************************************************/
/* Put the entire contents of a file out on a socket.  This function
 * is named after the UNIX "cat" command, because it might have been
 * easier just to do something like pipe, fork, and exec("cat").
 * Parameters: the client socket descriptor
 *             FILE pointer for the file to cat */
/**********************************************************************/
void cat(int client, FILE *resource)
{
    char buf[1024];

    fgets(buf, sizeof(buf), resource);
    while (!feof(resource)) {
        send(client, buf, strlen(buf), 0);
        fgets(buf, sizeof(buf), resource);
    }
}

/**********************************************************************/
/* Inform the client that a CGI script could not be executed.
 * Parameter: the client socket descriptor. */
/**********************************************************************/
void cannot_execute(int client)
{
    char buf[1024];
    sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-type: text/html\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<P>Error prohibited CGI execution.\r\n");
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Print out an error message with perror() (for system errors; based
 * on value of errno, which indicates system call errors) and exit the
 * program indicating an error. */
/**********************************************************************/
void error_die(const char *sc)
{
    perror(sc);
    exit(1);
}

/**********************************************************************/
/* Execute a CGI script.  Will need to set environment variables as
 * appropriate.
 * Parameters: client socket descriptor
 *             path to the CGI script */
/**********************************************************************/
void execute_cgi(int client, const char *path,
                 const char *method, const char *query_string)
{
    char buf[1024];
    int cgi_output[2];
    int cgi_input[2];
    pid_t pid;
    int status;
    int i;
    char c;
    int numchars = 1;
    int content_length = -1;

    buf[0] = 'A'; buf[1] = '\0';
    if (strcasecmp(method, "GET") == 0) {
        while ((numchars > 0) && strcmp("\n", buf)) {  /* read & discard headers */
	    	numchars = get_line(client, buf, sizeof(buf));
		}
    }
    else {    /* POST */
        numchars = get_line(client, buf, sizeof(buf));
		while ((numchars > 0) && strcmp("\n", buf)) {
	    	buf[15] = '\0';
	    	if (strcasecmp(buf, "Content-Length:") == 0) {
		    	content_length = atoi(&(buf[16]));
	    	}
	    	numchars = get_line(client, buf, sizeof(buf));
		}
		if (content_length == -1) {
	    	bad_request(client);
	    	return;
		}
    }

    sprintf(buf, "HTTP/1.0 200 OK\r\n");
    send(client, buf, strlen(buf), 0);

    if (pipe(cgi_output) < 0) {
        cannot_execute(client);
		return;
    }
    if (pipe(cgi_input) < 0) {
		cannot_execute(client);
		return;
    }

    if ( (pid = fork()) < 0 ) {
        cannot_execute(client);
		return;
    }
    // 子进程执行 CGI 脚本
    if (pid == 0) {  /* child: CGI script */
        char meth_env[255];
		char query_env[255];
		char length_env[255];

		dup2(cgi_output[1], 1); 	// 子进程标准输出定向到 cgi_output[1]
		dup2(cgi_input[0], 0); 		// 子进程标准输入定向到 cgi_input[0]
		close(cgi_output[0]);
		close(cgi_input[1]);
		sprintf(meth_env, "REQUEST_METHOD=%s", method);
		putenv(meth_env);
		if (strcasecmp(method, "GET") == 0) {
	    	sprintf(query_env, "QUERY_STRING=%s", query_string);
	    	putenv(query_env);
		}
		else {   /* POST */
	    	sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
	    	putenv(length_env);
		}
		execl(path, path, NULL);	// 子进程执行 CGI 脚本
		exit(0);
    } 
    else {    /* parent */
        close(cgi_output[1]);
        close(cgi_input[0]);
		if (strcasecmp(method, "POST") == 0) {
	    	for (i = 0; i < content_length; i++) {
	        	recv(client, &c, 1, 0);
				write(cgi_input[1], &c, 1);
	    	}
			// 从管道 cgi_output[0] 读到子进程处理后的信息，发送给客户端
	    	while (read(cgi_output[0], &c, 1) > 0) {
				send(client, &c, 1, 0);
	    	}
		}
		close(cgi_output[0]);
		close(cgi_input[1]);
		waitpid(pid, &status, 0);
    }
}

/**********************************************************************/
/* Get a line from a socket, whether the line ends in a newline,
 * carriage return, or a CRLF combination.  Terminates the string read
 * with a null character.  If no newline indicator is found before the
 * end of the buffer, the string is terminated with a null.  If any of
 * the above three line terminators is read, the last character of the
 * string will be a linefeed and the string will be terminated with a
 * null character.
 * Parameters: the socket descriptor
 *             the buffer to save the data in
 *             the size of the buffer
 * Returns: the number of bytes stored (excluding null) */
/**********************************************************************/
int get_line(int sock, char *buf, int size)
{
    int i = 0;
    char c = '\0';
    int n;

    while ((i < size - 1) && (c != '\n')) {
        n = recv(sock, &c, 1, 0);
	/* DEBUG printf("%02X\n", c); */
	if (n > 0) {
	    if (c == '\r') {
	        n = recv(sock, &c, 1, MSG_PEEK);
		/* DEBUG printf("%02X\n", c); */
		if ((n > 0) && (c == '\n'))
		    recv(sock, &c, 1, 0);
		else
		    c = '\n';
	    }
	    buf[i] = c;
	    i++;
	}
	else
	    c = '\n';
    }
    buf[i] = '\0';
    return(i);
}

/**********************************************************************/
/* Return the informational HTTP headers about a file. */
/* Parameters: the socket to print the headers on
 *             the name of the file */
/**********************************************************************/
void headers(int client, const char *filename)
{
    char buf[1024];
    (void)filename;  /* could use filename to determine file type */

    strcpy(buf, "HTTP/1.0 200 OK\r\n");
    send(client, buf, strlen(buf), 0);
    strcpy(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/html\r\n");
    send(client, buf, strlen(buf), 0);
    strcpy(buf, "\r\n");
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Give a client a 404 not found status message. */
/**********************************************************************/
void not_found(int client)
{
    char buf[1024];

    sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/html\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<BODY><P>The server could not fulfill\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "your request because the resource specified\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "is unavailable or nonexistent.\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</BODY></HTML>\r\n");
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Send a regular file to the client.  Use headers, and report
 * errors to client if they occur.
 * Parameters: a pointer to a file structure produced from the socket
 *              file descriptor
 *             the name of the file to serve */
/**********************************************************************/
void serve_file(int client, const char *filename)
{
    FILE *resource = NULL;
    int numchars = 1;
    char buf[1024];

    buf[0] = 'A'; buf[1] = '\0';
    while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
        numchars = get_line(client, buf, sizeof(buf));

    resource = fopen(filename, "r");
    if (resource == NULL)
        not_found(client);
    else {
        headers(client, filename);	// 发送 HTTP 响应头信息
        cat(client, resource);		// 发送 index.html 文件内容给客户端
    }
    fclose(resource);
}

/**********************************************************************/
/* This function starts the process of listening for web connections
 * on a specified port.  If the port is 0, then dynamically allocate a
 * port and modify the original port variable to reflect the actual
 * port.
 * Parameters: pointer to variable containing the port to connect on
 * Returns: the socket */
/**********************************************************************/
int startup(u_short *port)
{
    int httpd = 0;
    struct sockaddr_in name;
	// 建立套接字
    httpd = socket(PF_INET, SOCK_STREAM, 0); // 使用 IPv4 面向连接的数据传输方式
    if (httpd == -1) {
        error_die("socket");
    }
    memset(&name, 0, sizeof(name));
    name.sin_family = AF_INET;        // 使用 IPv4 地址
    name.sin_port = htons(*port);     // 端口
    name.sin_addr.s_addr = htonl(INADDR_ANY);    // ip地址
	// 将该套接字与IP地址和端口绑定
    if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0) {
        error_die("bind");
    }
	
	// 动态申请一个端口
    if (*port == 0) {
    	socklen_t namelen = sizeof(name);
        if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
            error_die("getsockname");
        *port = ntohs(name.sin_port);
    }
	// 让套接字进入被动监听状态，请求队列长度 5
    if (listen(httpd, 5) < 0) {
        error_die("listen");
    }
    return httpd;
}

/**********************************************************************/
/* Inform the client that the requested web method has not been
 * implemented.
 * Parameter: the client socket 
*/
/**********************************************************************/
// 客户端请求web方法无效
void unimplemented(int client)
{
    char buf[1024];

    sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/html\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</TITLE></HEAD>\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</BODY></HTML>\r\n");
    send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                          void *(*start_routine) (void *), void *arg);
*/

int main(void)
{
    int server_sock = -1;
    u_short port = 0;    // 定义端口
    int client_sock = -1;
    struct sockaddr_in client_name;
    socklen_t client_name_len = sizeof(client_name);
    pthread_t newthread;

    // 建立服务端套接字，并处于监听状态
    server_sock = startup(&port);
    printf("httpd running on port %d\n", port);

    while (1) {
        // 接收客户端请求
        client_sock = accept(server_sock, (struct sockaddr *)&client_name, &client_name_len);
        if (client_sock == -1) {
            error_die("accept");
        }
		
        // 开辟新的线程来运行线程函数 accept_request
        if (pthread_create(&newthread , NULL, accept_request, (void *)&client_sock) != 0) {
	        perror("pthread_create");
        }
    }
    close(server_sock);
    return(0);
}
